A new Wolf-Rayet star and its circumstellar nebula in Aquila★

Abstract

We report the discovery of a new Wolf–Rayet star in Aquila via detection of its circumstellar nebula (reminiscent of ring nebulae associated with late WN stars) using the Spitzer Space Telescope archival data. Our spectroscopic follow-up of the central point source associated with the nebula showed that it is a WN7h star (we named it WR 121b). We analysed the spectrum of WR 121b by using the Potsdam Wolf–Rayet model atmospheres, obtaining a stellar temperature of ≃50 kK. The stellar wind composition is dominated by helium with ∼20 per cent of hydrogen. The stellar spectrum is highly reddened [E(B−V) = 2.85 mag]. Adopting an absolute magnitude of Mv=−5.7, the star has a luminosity of log L/L⊙= 5.75 and a mass-loss rate of 10−4.7 M⊙ yr−1, and resides at a distance of 6.3 kpc. We searched for a possible parent cluster of WR 121b and found that this star is located at ≃1° from the young star cluster embedded in the giant H ii region W43 (containing a WN7+a/OB? star – WR 121a). We also discovered a bow shock around the O9.5III star ALS 9956, located at from the cluster. We discuss the possibility that WR 121b and ALS 9956 are runaway stars ejected from the cluster in W43.